Opencv Python 简明教程

OpenCV Python - Draw Shapes and Text

在本章中，我们将学习如何在 OpenCV-Python 的帮助下在图像中绘制形状和文本。让我们从了解在图像上绘制形状开始。

In this chapter, we will learn how to draw shapes and text on images with the help of OpenCV-Python. Let us begin by understanding about drawing shapes on images.

Draw Shapes on Images

我们需要了解 OpenCV-Python 中所需的函数，这有助于我们绘制图像上的形状。

We need to understand the required functions in OpenCV-Python, which help us to draw the shapes on images.

Functions

OpenCV-Python 程序包（称为 cv2）包含以下用于绘制相应形状的函数。

The OpenCV-Python package (referred as cv2) contains the following functions to draw the respective shapes.

Function

Description

Command

cv2.line()

Draws a line segment connecting two points.

cv2.line(img, pt1, pt2, color, thickness)

cv2.circle()

Draws a circle of given radius at given point as center

cv2.circle(img, center, radius, color, thickness)

cv2.rectangle

Draws a rectangle with given points as top-left and bottom-right.

cv2.rectangle(img, pt1, pt2, color, thickness)

cv2.ellipse()

Draws a simple or thick elliptic arc or fills an ellipse sector.

cv2.ellipse(img, center, axes, angle, startAngle, endAngle, color, thickness)

Parameters

以上函数的通用参数如下 −

The common parameters to the above functions are as follows −

Sr.No.

Function & Description

1

img The image where you want to draw the shapes

2

color Color of the shape. for BGR, pass it as a tuple. For grayscale, just pass the scalar value.

3

thickness Thickness of the line or circle etc. If -1 is passed for closed figures like circles, it will fill the shape.

4

lineType Type of line, whether 8-connected, anti-aliased line etc.

Example

以下示例显示如何在图像上绘制形状。程序如下 −

Following example shows how the shapes are drawn on top of an image. The program for the same is given below −

import numpy as np
import cv2
img = cv2.imread('LENA.JPG',1)
cv2.line(img,(20,400),(400,20),(255,255,255),3)
cv2.rectangle(img,(200,100),(400,400),(0,255,0),5)
cv2.circle(img,(80,80), 55, (255,255,0), -1)
cv2.ellipse(img, (300,425), (80, 20), 5, 0, 360, (0,0,255), -1)
cv2.imshow('image',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

Output

draw shapes

Draw Text

提供 cv2.putText() 函数在图像上写文本。命令如下 −

The cv2.putText() function is provided to write a text on the image. The command for the same is as follows −

img, text, org, fontFace, fontScale, color, thickness)

Fonts

OpenCV 支持以下字体 −

OpenCV supports the following fonts −

Font Name

Font Size

FONT_HERSHEY_SIMPLEX

0

FONT_HERSHEY_PLAIN

1

FONT_HERSHEY_DUPLEX

2

FONT_HERSHEY_COMPLEX

3

FONT_HERSHEY_TRIPLEX

4

FONT_HERSHEY_COMPLEX_SMALL

5

FONT_HERSHEY_SCRIPT_SIMPLEX

6

FONT_HERSHEY_SCRIPT_COMPLEX

7

FONT_ITALIC

16

Example

以下程序为照片添加文本标题，照片中是著名的足球运动员莱昂内尔·梅西。

Following program adds a text caption to a photograph showing Lionel Messi, the famous footballer.

import numpy as np
import cv2
img = cv2.imread('messi.JPG',1)
txt="Lionel Messi"
font = cv2.FONT_HERSHEY_SIMPLEX
cv2.putText(img,txt,(10,100), font, 2,(255,255,255),2,cv2.LINE_AA)

cv2.imshow('image',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

Output

draw text